1. Summary of the Invention
This application relates to finned tubes for and, more particularly, to air-cooled heat exchange equipment condensing steam or other such vapors that employ extended-surface fins attached by metallurgical bonding to fluid-flowing tubes.
2. Summary of the Background Art
This application describes the design and fabrication of finned tube of the type used but not described in U.S. Pat. No. 5,139,083 issued Aug. 18, 1992. More specifically, the invention of the instant application relates to cost-related improvements in the design and fabrication of metallurgically-bonded finned tubes that are used in the assembly of air-cooled heat exchange bundles. These are the bundles which make up the bulk of air-cooled steam condensers of the type employed in steam-electric power generating stations. The turbine exhaust steam is condensed inside these bundles by forced ambient air flowing over the finned tubes and the condensate is returned to the power plant cycle. In a large power plant there may be as much as 100 miles of such finned tubes condensing the exhaust steam.
The recent trend in bundle design and construction has been toward the use of large tubes with only one or two rows depth. Large single-row tubes are more freeze proof and can be more economic in manufacturing and in their structural support. In addition to low cost and freeze protection, there are the additional goals pursued by manufacturers which are the atmospheric corrosion protection of the fins and tubes and their long term heat transfer rate stability between the tubes and fins. Experience has shown that the most stable fin-tube construction has been found to be the fins that are metallurgically bonded to the tube. The most popular metallurgical bonding process is hot-dip galvanizing in which both the tube and the fins are of steel material. A new bonding process recently used in this field is that of furnace brazing aluminum fins to an aluminized steel tube with a layer of aluminum-silica.
Currently there are two types of steel fin-tube designs that employ hot-dip galvanizing. One uses press-punched fins that are installed by sliding them individually over a horizontal oval-shaped tube and the second type uses a machine that wraps a spiral fin around an oval-shaped tube. Both the methods have their manufacturing problems at high production rates. The problems, however, disappear at lower production rates but at a penalty of higher unit costs.
The more obvious background patents in the field of large steam condensing tubes and bundles are listed below with brief comment on their design features.
1. RUFF, U.S. Pat. No. 3,976,126 has many similar construction features as this application. Its fins, however, envelope the complete tube and are installed over the end of the bare tube. During assembly these fins must be loose enough to slide over the tube yet tight enough to have the fin-tube gap closed by zinc in the hot-dip galvanizing process. Manufacturing dimensional tolerances of the tube make this a very difficult procedure because the fins tend to get hung-up on tight spots that are over-tolerance on the tube during the fin-stacking process. Also, there is a large wastage of sheet metal material in the punching of the oval shaped opening in the fin. This is costly considering that an air-cooled steam condenser serving a large power plant may have over 50 million such fins in a single row bundle design. PA1 2. SAPERSTEIN, U.S. Pat. No. 4,256,177 describes a serpentine fin design and a furnace brazing bonding operation currently used by a condenser manufacturer. The fins are brazed to the two sides of a rectangular shaped tube. There is one fin assembly per tube side and the brazing is done with the fin assembly placed on top of the tube. PA1 3. KLUPPEL, U.S. Pat. No. 4,168,742 shows a tube with parallel side walls and fins in the form of pleats secured to the sides of adjacent tubes. The manufacturing and bonding process of this tube is not described or discussed. PA1 4. GREEVER, U.S. Pat. No. 4,102,027 describes a fin design that is spirally wound about a tubular element with metal-to-metal contact produced by tension forces. PA1 5. HARADA, U.S. Pat. No. 3,916,989 PA1 6. FORGO, U.S. Pat. No. 3,135,320 PA1 7. GUNTER, U.S. Pat. No. 3,438,433 PA1 8. WAGNER, British Patent No. 359,102 reveals a finned tube for radiator applications that has an elongated tube and a slotted fin similar to this application. The difference between the two is the design techniques employed to mechanically hold the fins onto the tubes. Wagner holds his fins against the flat walls of the tube by forcing the fins to flex the thin-walled tubes inward slightly. Larinoff employs a middle fin link to mechanically hold the fins into the tubes. PA1 9. KASE, Japan Patent No. 4-43292, has a refrigeration finned tube similar in basic design as Wagner and Larinoff. Kase holds his fins against the flat walls of the tube by the flexing of the 90 degree, bend between the fins and their collars.
All three of the above patents describe plate-fin type air-cooled heat exchangers that envelope one or more tubes.
Accordingly, it is the object of the present invention to design a fin for a large rectangular shaped tube that is low cost because its design layout is highly efficient in the use of the raw sheet metal material from which the fins are machine punched.
It is the further object of the present invention to devise simple means of mechanically holding the fin onto the tube prior to the metallurgical bonding of the fins to the tube.
It is the further object of the present invention to devise a simple and low cost assembly process for coupling the fins onto the tubes.
It is a further object of the present invention to design and install the finned tubes into condense bundles such as to provide added freeze protection to the condensate draining inside the tubes.
As regards the first object shown above, typical fins on the market today look like U.S. Pat. Nos. 3,976,126 and 4,997,036, copy attached, where the metal material that is punched out to allow for the insertion of the large tube, is scrapped.
The foregoing has outlined some of the more pertinent objects of the present invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results could be obtained by applying the disclosed invention in a different manner or modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description of the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.